This invention relates to friction brake assemblies, particularly of the type having axially aligned alternating rotatable and stationary brake disks carried between and axially movable between a pressure plate and a reaction plate, and more particularly to an improved friction disk for use in such an assembly, suitable, for use in the brake stack of an aircraft wheel and brake assembly.
Carbon brake disks have come to be employed in many aircraft braking applications. The carbon material of which these disks are formed is very costly to manufacture. Such carbon or graphite disks have been commonly discarded when the friction surfaces of the disk are sufficiently worn. Many techniques have been proposed to maximize utilization of this expensive carbon material. Such prior art efforts include replacement of a single full thickness disk with two disks of reduced thickness (Article entitled "The Economic and Safety Aspects of Commercial Carbon Brakes", Apr. 18-21, 1982 by L. FitzGerald and B. Lockwood-Goose), riveting carbon wear plates to a structural carbon or graphite core disk (U.S. Pat. Nos. 3,712,427 and 3,800,392 and to Cook et al.), riveting carbon wear facings to a core disk formed of beryllium segments (U.S. Pat. No. 3,731,769 to Ely), bonding new friction facings to the carbon core of a used disk (GB 2148187B), and splitting two worn disks to form two thinner half disks and bonding one of them to each side of a carbon core to form a new disk (U.S. Pat. No. 4,982,818 to Pigford). Notwithstanding the foregoing efforts, there remains a desire to enhance carbon utilization.
The present invention provides a friction disk in which the wear surface(s) of the disk is/are mechanically attached to the associated carrier and may be renewed by replacement, and the structural core carrier can be reused, and a method for refurbishing such friction disk. The carrier includes an annular strap with a plurality of legs extending radially therefrom thereby forming a plurality of circumferentially spaced apart recesses. The obverse face of the lining (obverse to the friction face) includes raised areas of a shape that is complementary to the shape of the recesses of the carrier. The raised areas of the lining matingly engage the walls of the recesses of the carrier thereby locating the lining and providing a large bearing surface for transfer of torque during a braking action, thereby preventing rotation of the lining relative to the carrier. The forces generated during a braking action are transmitted from the lining to the core through shear loading of a large area of the the lining material compared to prior art methods. In these preferred embodiments, the braking forces are are not transferred through the fasteners which retain the lining in position on the core. The carrier may be formed of metal, carbon or other material capable of retaining sufficient structural properties at the temperatures to be encountered in service. The lining material may be formed from carbon friction material remaining after any use of any of the foregoing prior art methods or from virgin carbon or ceramic material.
In comparison to conventional steel aircraft brakes, preferred embodiments of disk assemblies according to the invention have increased resistance to bending or deformation from the desired flat configuration during a high energy braking action such may occur during a rejected takeoff of an aircraft. This increased resistance to bending from the desired flat configuration contributes to maintenance of a more uniform clamp load distribution across the full face of the brake stack or heat sink and structural integrity of the brake stack or heat sink during such high energy braking action.